1. Field of the Invention
The present invention relates to a digital camera and particularly to the control of power supply of a digital camera connected to a data processing device such as a personal computer.
2. Description of the Background Art
When displaying or browsing an image photographed by a digital camera, data representative of the photographed image is usually transferred for editing to a data processing device such as a personal computer. An image photographed by a digital camera is transferred to a personal computer, for example, in the following ways: (1) multiple frames are once stored in the image memory of the camera and then, via a cable or a memory card, transferred to an external personal computer, or (2) image data captured by a digital camera is transferred directly to a personal computer, almost at the same time the image is photographed, via a high-speed digital interface between the digital camera and the personal computer. An example of the latter is disclosed in Japanese Patent Laid-Open Publication Nos. 121147/1995 and 163209/1997.
Japanese Patent Laid-Open Publication No. 121147/1995 discloses an integrated structure of a video camera and a personal computer, in which digital signals generated in the camera are directly transferred to the personal computer. When transferring digital signals from the camera to the personal computer at a higher transmission rate, this method uses a connector structure that does not include a cable and the like as a transmission line but connects, directly in a short distance, the camera to the personal computer to reduce a waveform distortion that might have been caused by the resistance and/or the parasitic capacitance of the transmission line, and to reduce a high-frequency noise radiation during high-speed data transfer. The integrated structure of the camera and the personal computer eliminates an image memory from being installed in a camera, resulting in a reduced cost. However, because the camera is powered by the battery of the personal computer, extending the available time as a whole of the camera and personal computer requires proper power management when both are used as portable equipment.
Japanese Patent Laid-Open Publication No. 163209/1997 discloses a digital camera system that controls the photographing operation of the digital camera in response to control signals from a data processing device connected to the digital camera. To transfer digital data from the camera to a personal computer at a high speed, this system uses, for example, a general-purpose parallel-port PCMCIA standard interface intended for personal computers, and an in-camera power-on control command sent from the personal computer via the interface in response to an instruction from the operator in order to take a picture. This system keeps camera powered on only when the camera operator issues an instruction, and keeps the same powered off in other cases, to minimize power consumption.
Both of the prior-art technologies described above implement the digital camera function on such a way that a digital camera unit (imaging function) and a data processing device such as a personal computer, connected to the camera unit, work together. The digital camera unit and the personal computer when working together increase operability and reduce power consumption.
However, in the prior art, the photographing part and the personal computer must be interconnected to configure a digital camera as a whole in order to implement the digital camera function. Therefore, when taking a picture, both the digital camera and the personal computer are required. Because photographing and recording cannot be executed by a camera only, the system in the prior art is extremely inconvenient as a portable system.
It is an object of the present invention to provide a digital camera that overcomes the aforementioned drawbacks encountered in the prior art and that reduces the consumption of a power supply within the digital camera.
It is another object of the present invention to provide a digital camera that does not necessarily require a special AC charging-adapter or a special charging unit.
In accordance with the present invention a digital camera for photographing a subject to output image signals representing the subject comprises an interface connectable to an external data processing device, and transferring the image signals to the data processing device; an internal power supply supplying first power to components of the digital camera; an external power receiving circuit receiving second power from the data processing device; a first switching circuit selectively switching between the internal power supply and the external power receiving circuit to supply the first or second power to the components of the digital camera; a connection detection circuit detecting that the data processing device has been connected to the interface; and a control circuit controlling the first switching circuit in response to the connection detection circuit, wherein the control circuit controls the first switching circuit in such a way that, when the connection detection circuit does not detect that the interface is connected to the data processing device, the first power is supplied to the components of the digital camera and, when the connection detection circuit detects that the interface is connected to the data processing device, the internal power supply is disconnected and the second power is supplied to the components of the digital camera.
Specifically, the digital camera in accordance with the present invention operates as follows. For example, when the digital camera is connected to an external data processing device, such as a personal computer, to transfer a photographed digital image to the data processing device, the connection detection circuit determines when the digital camera is connected to the data processing device. Then, the power is supplied from the data processing device to the components of the digital camera to start feeding the components of the digital camera, and to activate the communication with the data processing device. After this, image data may be transferred from the digital camera under the control of the data processing device. Then, the power fed from the internal power supply within the digital camera is turned off so that the internal power supply will not be used, thus minimizing the consumption of the battery.
When the digital camera is connected to the data processing device without transferring image data, the power fed to the components of the digital camera is turned off under the control of the data processing device. In this case, the digital camera will enter the standby state and allow the charging circuit to receive power from the data processing device to charge the secondary battery of the digital camera.
In addition, even when the digital camera is connected to the data processing device to transfer image data, connecting the internal power supply to the charging circuit under the control of the data processing device allows power to be supplied from the data processing device not only to feed the components of the camera but also to charge the second battery of the internal power supply, thereby increasing efficiency more.
Thus, the digital camera in accordance with the present invention, which is adapted to be detachable from a data processing device such as a personal computer when a picture is taken, has the camera function not only for photographing but also for processing signals and storing image data, and is suitable to carry. In addition, when image data is transferred, the digital camera receives power supplied from the data processing device to be turned on the consumption of the power supply within the digital camera being minimized.
The present invention provides a digital camera capable of transferring digital image data, which is photographed by the digital camera, to an external data processing device at a high speed, wherein the digital camera is convenient for carrying, thus minimizing the consumption of the battery in the camera. Also, with the digital camera connected to the external data processing device, the secondary battery in the digital camera may be efficiently charged while the camera is idle, for example, image data is not being transferred.
In addition, with power supplied from the external data processing device, the digital camera may be used not only in the image data transfer mode but also in the photographing mode under the control of the external data processing device.